<style>
    #box-container {
        display: flex;
        height: 500px;
    }
    #box-1 {
        background-color: dodgerblue;
        order: 2;
        height: 200px;
        width: 200px;
    }

    #box-2 {
        background-color: orangered;
        order:1;
        height: 200px;
        width: 200px;
    }
</style>

<div id="box-container">
    <div id="box-1"></div>
    <div id="box-2"></div>
</div>